Trees, shrubs and flowers could soon dot the roofs of certain newconstruction projects across Toronto, if City Hall gets its way.

Undera proposed bylaw before the planning and growth committee next week,the city would require a "green roof" on any office building or retailplaza bigger than 5,000 square metres (about 53,000 square feet), aswell as on most condominium buildings higher than seven storeys.

Theretail dimensions are about half the size of a regular Canadian Tirestore, said Jane Welsh, the city's acting project manager forenvironmental planning. Green coverage of a roof could vary between 30and 60 per cent, depending on building size.

"If Toronto wants to be aleader, then lead" and don't deal in half-measures, said Steven Peck atGreen Roofs for Health Cities, a non-profit industry association.

"I don't understand why businesses in the public realm have been exempted."

Other jurisdictions may cite Toronto's example to exempt many classes of buildings, Peck argued.

Greenroofs can act much like parks to reduce the "urban heat island" effect,in which built-up areas become several degrees warmer in summer thansurrounding areas. That contributes to smog and raises the energy billfor air conditioning.

While green roofs cost more to install – anextra $10 to $40 per square foot – they can double its life byproviding shelter from extremes of cold and heat.

The insulation also brings energy savings, winter and summer.

"We have serious reservations about this bylaw," said planner Steve Daniels at Tridel, whose condo projects would be affected.

Anotherbylaw requires outdoor amenity space in condo towers, he noted, whilegreen roofs must be irrigated and cannot be walked on for the first twoyears.